Prior optical element installation devices have ranged from adhesive bonding of the lens in its barrel or mounting tube to precision machined contoured and threaded retaining rings which engage in the lens mounting barrel and against the lens. Considering the centerline line-of-sight as being the lens axis, there have been various ways of axially securing a lens in a barrel. For example, the lens may engage against a rigid shoulder in the lens barrel and be retained thereagainst by different structures. For example, a snap ring can engage in a groove in the barrel and engage against the lens to hold it against a shoulder. A thin rim may be spun down against the lens to hold it against a shoulder. A male threaded ring may engage a female thread within the barrel and directly bear against the lens to hold it against a shoulder. When resiliency is desired, an elastomeric ring, such as an elastomeric O-ring, made of rubberlike material, can be placed between the lens and its clamp ring.
For radially centering the lens within its support barrel, an elastic material in the form of a ring may provide the necessary support. This elastic material may be molded and placed around the lens or may be injected around the lens after it is in position.
The problem in precision lens mounting is that the lenses or other optical elements have a substantially different thermal coefficient of expansion than the metal or polymer barrel in which they are mounted. When temperature cycling occurs, the lenses and other optical elements may shift and lose their optical alignment. Rigid structures are desirable to achieve and maintain this optical alignment, but the compressive forces generated by such temperature cycling dictate against rigid mounting because brittle optical elements can crack from the stresses resulting from temperature-induced dimensional changes. Shock and vibration tend to displace optical components, so firm mounting is required. Thus, there is need for a lens mounting configuration which maintains axial and radial alignment of the optical elements mounted thereby during vibration and thermal dimensional changes in order to provide a rugged optical system of good precision and long life.